I don't always keep them either. One thing that helps me tremendously though is Ravelry. Because I put in most of my projects I can look back at what yarn and needle size I used for each. Even if I don't remember the name of the yarn I know that something I made was from it so I can go back and look. This doesn't help you now, but maybe in the future?

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Jan

When asking questions ALWAYS post the name and a link for the pattern if you have it.